Jaguar is a petascale supercomputer built by Cray at Oak Ridge National Laboratory in Oak Ridge, Tennessee. As of November 2009, it was the world's fastest computer with a peak performance of more than 1750 teraflops (1.75 petaflops). A Cray XT5 system, Jaguar has 224,256 Opteron processor cores, and operated with a version of Linux called Cray Linux Environment.

Moore's Law and economies of scale are the dominant factors in supercomputer design: a single modern desktop PC is now more powerful than a ten-year-old supercomputer, and the design concepts that allowed past supercomputers to out-perform contemporaneous desktop machines have now been incorporated into commodity PCs. Furthermore, the costs of chip development and production make it uneconomical to design custom chips for a small run and favor mass-produced chips that have enough demand to recoup the cost of production.

A current model quad-core Xeon workstation running at 2.66 GHz will outperform a multimillion dollar Cray C90 supercomputer used in the early 1990s; most workloads requiring such a supercomputer in the 1990s can now be done on workstations costing less than 4,000 US dollars. Supercomputing is taking a step of increasing density, allowing for desktop supercomputers to become available, offering the computer power that in 1998 required a large room to require less than a desktop footprint.

The National Center for Computational Sciences (NCCS), sponsored by the Department of Energy's (DOE) Office of Science, manages Oak Ridge National Laboratory's (ORNL) Jaguar supercomputer for use by scientists and engineers solving problems of national and global importance. The machine, with a peak performance of more than two petaflops, makes it possible to address some of the most challenging scientific problems in areas such as climate modeling, renewable energy, materials science, fusion and combustion. Annually, 80 percent of Jaguar's resources are allocated through DOE's Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program, a competitively selected, peer reviewed process open to researchers from universities, industry, government and non-profit organizations.

Through a close, four-year partnership between ORNL and Cray, Jaguar has delivered state-of-the-art computing capability to scientists and engineers from academia, national laboratories and industry. The XT system has grown in strength through a series of advances since being installed as a 25-teraflop XT3 in 2005. By early 2008 Jaguar was a 263-teraflop Cray XT4 able to solve some of the most challenging problems that could not be solved otherwise. In 2008 Jaguar was expanded with the addition of a 1.4-petaflop Cray XT5, and in fall 2009 the system was upgraded with Six-Core AMD Opteron processors, increasing the number of its processing cores to more than 224,000, connected internally with Cray's SeaStar2+ network. The XT4 and XT5 parts of Jaguar are combined into a single system using an InfiniBand network that links each piece to the Spider file system.

In November 2009, Jaguar was named #1 on the Top500 list of the world's most powerful computers.

Throughout its series of upgrades, Jaguar has maintained a consistent programming model for the users. This programming model allows users to continue to evolve their existing codes rather than write new ones. Applications that ran on previous versions of Jaguar can be recompiled, tuned for efficiency, and then run on the new machine.

Jaguar is the most powerful computer system for science with world leading performance, more than three times the memory of any other computer, and world leading bandwidth to disks and networks. The AMD Opteron processor is a powerful, general purpose processor that uses the X86 instruction set which has a rich set of applications, compilers, and tools. Jaguar has hundreds of applications that have been ported and run on the Cray XT system, many of which have been scaled up to run on large numbers of cores. Jaguar takes on the most challenging problems in the world.